I'm wondering how would they react if it's revealed that anything short of divine intervention won't damage the ship?
At this point it probably wouldn't matter. As far as the world knows, nothing can damage them already - since they went against a regular navy of a nation capable of fighting on multiple fronts.
A fair point has been raised though - there's no mention of the ships cancelling inertia for the passengers, so if they can be launched like shown here with enough acceleration, then everyone on board is dead even though the vessel would be undamaged. I was thinking the only way to deal with them would be to get a fleet to ram and push them into some precarious position, like into a cave that would then be collapsed on top of it, trapping the crew until they starved to death, but this might be an option too.